The present disclosure generally relates to drilling fluids and, more specifically, to methods for determining the efficiency of gas extraction from a drilling fluid.
Treatment fluids may be used in a variety of subterranean treatment operations. Such treatment operations can include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, and the like. As used herein, the terms “treat,” “treatment,” “treating,” and grammatical equivalents thereof refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component thereof, unless otherwise specified herein. More specific examples of illustrative treatment fluids can include, for example, drilling fluids, fracturing fluids, gravel packing fluids, acidizing fluids, conformance fluids, scale dissolution and removal fluids, diverting fluids, and the like.
A drilling fluid or drilling mud is a designed fluid intended for circulation through a wellbore to facilitate a drilling operation. Functions of a drilling fluid can include, without limitation, removing drill cuttings from the wellbore, cooling and lubricating the drill bit, aiding in the support of the drill pipe and the drill bit, and forming a hydrostatic head to maintain integrity of the wellbore walls and/or to prevent blowouts from occurring. Drilling fluids may be water-based or oil-based and may sometimes be in the form of an emulsion.
Drilling fluids can also be analyzed to detect and/or quantify gaseous compounds being expelled from a wellbore in the course of a drilling operation. This information can be very valuable for a well operator. For example, analysis of gaseous wellbore compounds and their sequence of removal from a wellbore can help a well operator determine the geological profile of a subterranean formation penetrated by the wellbore. Although simply detecting the presence of particular gaseous compounds can sometimes provide sufficient information to a well operator, it can often be desirable to quantify the amount of gaseous compounds that are present in a drilling fluid sample.
It is frequently desirable to analyze for gaseous compounds following their removal from the drilling fluid. Removal of the gaseous compounds from the drilling fluid can take place through various degassing techniques, which may have varying degrees of extraction efficiency. As used herein, the term “extraction efficiency” will refer to the fraction of a gaseous compound withdrawn from a drilling fluid compared to the amount of the gaseous compound originally present in the drilling fluid. Degassing can often be incomplete, and the actual extent of degassing can be difficult to determine accurately. Incomplete degassing of a drilling fluid can therefore lead to an inaccurate determination of the amount of gaseous compounds actually present therein, which can subsequently lead to an incorrect analysis of the geological profile being encountered downhole. The consequences of inadequately determining the quantity of gaseous compounds that are present in a drilling fluid can range from costly inefficiency in the drilling process to extreme safety issues. For example, an incoming flux of hydrocarbon gas or hydrogen sulfide can help a well operator determine whether a drilling operation has gone as intended. Specifically, the identity and amount of a withdrawn wellbore gas can help a well operator determine if a geological stratum of interest has been reached during drilling.
Presently, there are limited ways to determine the absolute degassing efficiency of a drilling fluid, particularly for analyses conducted in-process. Many conventional degassing techniques subject a drilling fluid to multiple degassing cycles in sequence, and as the amount of withdrawn gaseous compounds drops below a threshold value, the degassing operation is presumed to be complete. However, significant quantities of gaseous compounds may still remain in the drilling fluid even after multiple degassing cycles have been completed, and the detected quantity of gaseous compounds may not be representative at all of the “true” quantity of gaseous compounds that are present. Moreover, from an operational standpoint, multiple degassing cycles can represent an inefficient use of a well operator's time and resources.